1. Field of the Invention
This invention relates to ink jet printing inks, and, more particularly, this invention relates to ink jet printing inks which are water based and utilize a fluorescent pigment and butyl carbitol in combination.
2. Brief Description of the Prior Art
In U.S. Pat. No. 3,596,275 issued to Sweet on July 27, 1976 and entitled, "Fluid Droplet Recorder," description is made of what is now known in the art as ink jet printing. The basic technique in ink jet printing involves the use of one or more nozzle assemblies connected to a pressurized ink source. Each nozzle includes a small orifice, usually having a diameter on the order of about 0.0015 to 0.0028 inches, which is energized or modulated by an electromechanical transducer to emit a continuous stream of uniform ink drops at a rate on the order of 20 to 200 kilohertz. The stream of droplets is directed onto the surface of a moving writing medium, for example, paper.
Ink jet printers are adapted for making a record on a writing medium by generating a series of ink drops, applying a charge successively on each of the ink drops in response to a signal which is received by the printer. These drops are then directed along a path between two parallel conductive plates. A deflection field, which is generated at a bias potential, is applied to these plates with the result that the ink drops are deflected so that they reach the writing medium (or the material). They provide a representation characteristic of the information contained in the signals. The general configuration of ink systems employed within ink jet printers includes an ink sump or reservoir which stores ink. The sump feeds a compressor which in turn feeds a conduit, which is connected to a nozzle. An electromechanical transducer is employed to vibrate the nozzle at some suitable, high frequency, which after the ink is ejected through an orifice of the nozzle in a stream, causes the stream to break into individual drops. It is desired for proper charging of the individual drops that the breakup of the stream occur within the charging slot. The charging slot is the most desirable point along the path of the stream for the actual charge on each individual drop to be placed.
It can be seen from this brief description of ink jet printing systems that the ink used must possess a unique combination of properties. The primary parameter considered in formulating ink jet printing ink should be having a viscosity for the ink within the range of about 1.0 to 10.0 centipoise at 75.degree. F. and preferably 2.0 to 6.0 centipoise. As will be appreciated by those skilled in the art, the viscosity of the composition varies somewhat with the nature of the particular ink jet printing apparatus.
It is desirable that the ink used in ink jet printing be recycled. In other words, the ink drops which are not used to print on the writing medium are collected in a drain and returned to the ink sump. The ink is again pressurized and moves through the conduit and toward the nozzle. If the ink is not utilized for writing purposes it collects in the drain again and returns to the sump. During its transit between the nozzle and the drain ink is exposed to the ambient air. Evaporation can and does occur. It is well known in the art that the viscosity of the ink is one of the major parameters which determines the location along the path of the stream of ink where the breakup into individual drops occurs. The volume, distribution, and shape of drops are also viscosity influenced. A change in the viscosity of the ink (or writing fluid) causes the point at which the breakup occurs to be altered which in turn effects the charging of the drops in response to the signal present on the charging slot. The magnitude of the deflection of each individual drop is directly related to its particular charge. Thus, a change in the breakup point of the drops will alter the point of impact of the individual drops onto the writing medium.
In order to improve the contrast between the writing medium and the ink, it is desirable that the ink be fluorescent for certain application such as optical reading systems. The use of organic fluorescent pigments in various fields is well known as shown in U.S. Pat. No. 2,940,937 issued to O'Brien on June 14, 1960 and entitled "Fluorescent Printing Ink." The formulation of dye stuffs involves curing of resinous material, followed by the grinding of the mass into a powder.
Further it is highly desirable that the ink utilized be nonflammable. The heat generated in a high speed transport with intensive illumination etc. can be so high as to ignite flammable inks. It is therefore desirable that water based inks be utilized in ink jet printing and that those water based inks be nonflammable.
Because the orifice diameters of the nozzle are on the order of 0.0015 to 0.0028 inches, nozzle clogging can become a major problem. Therefore, the ink of an ink jet printing system can not contain particulate material which could clog the orifice of the nozzle nor can it be an ink which dries and plugs the orifice when the system is not in use.
An additional requirement for an ink jet printing ink is that is must be electrically conductive. It is also highly desirable that the ink not smear and have a relatively fast drying time. Since it is required that the ink not smear on the writing medium, the ink jet printing ink must have the property of being readily absorbed into the writing medium. In other words the ink must have the characteristic of wetting. Wetting is the property of a liquid describing its ability to penetrate a writing medium as defined by a loss of reflectivity.
Various formulations of ink for ink jet printing systems are known in the arts such as U.S. Pat. No. 3,994,736 issued to Hertz et al on Nov. 30, 1976 and entitled "Ink Composition for Ink Jet Writing," U.S. Pat. No. 3,846,141 issued to Ostergren on Nov. 5, 1974 and entitled "Jet Printing Ink Composition," and U.S. Pat. application Ser. No. 804,429 by Redick and McJohnson filed on June 7, 1977 l and entitled "Fluorescent Jet Printing Ink Composition."
None of the prior compositions are fluorescent aqueous inks for ink jet printing which are nonflammable and have a relatively short time for absorbtion by the writing medium. Additionally, the prior constructions do not show a fluorescent ink for ink jet printing which is both nonflammable and has a brief wetting time and in addition has relatively small changes in viscosity when utilized over a relatively long period of time in an ink recycling system within an ink jet printer.